Pension and Other Postretirement Benefits (Details 6) (USD $) In Millions, unless otherwise specified	Apr. 30, 2012	Apr. 30, 2011
Funded status is recorded on the accompanying consolidated balance sheets
Accounts payable and accrued expenses	$ (6)	$ (6)
Accrued postretirement benefits	(278)	(203)
Pension Benefits [Member]
Funded status is recorded on the accompanying consolidated balance sheets
Other assets	3	7
Accounts payable and accrued expenses	(3)	(3)
Accrued postretirement benefits	(219)	(150)
Net liability	(219)	(146)
Accumulated other comprehensive loss:
Net actuarial loss (gain)	346	263
Prior service cost	4	3
Total	350	266
Medical and Life Insurance Benefits [Member]
Funded status is recorded on the accompanying consolidated balance sheets
Accounts payable and accrued expenses	(3)	(3)
Accrued postretirement benefits	(59)	(53)
Net liability	(62)	(56)
Accumulated other comprehensive loss:
Net actuarial loss (gain)	1	(3)
Prior service cost	6	6
Total	$ 7	$ 3